introduction to accelerator physics superconducting magnets · introduction to accelerator physics...
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Introduction to Accelerator Physics Superconducting Magnets
Prague, Czech Republic
31 August - 12 September
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Overview
Why superconductors ? A motivation
A superconductor physics primer
Superconducting magnet design Superconducting cables
Superconducting magnets
The making of a superconducting magnet
Uses of superconductivity
A closing word
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Overview
Why superconductors ? A motivation
A superconductor physics primer
Superconducting magnet design Superconducting cables
Superconducting magnets
The making of a superconducting magnet
Uses of superconductivity
A closing word
![Page 4: Introduction to Accelerator Physics Superconducting Magnets · Introduction to Accelerator Physics Superconducting Magnets Luca.Bottura@cern.ch Prague, Czech Republic 31 August -](https://reader031.vdocuments.mx/reader031/viewer/2022040408/5eb93ddd29730e429c60ed22/html5/thumbnails/4.jpg)
1
10
100
1000
10000
0 2 4 6 8 10Field (T)
Cu
rre
nt d
ensity (
A/m
m2)
Conventional iron
electromagnets
Nb-Ti
Why superconductivity anyhow ?
Abolish Ohm’s law ! no power consumption (although
need refrigeration power)
high current density
ampere turns are cheap, so don’t need iron (although often use it for shielding)
Consequences lower running cost new
commercial possibilities
energy savings
high current density smaller, lighter, cheaper magnets reduced capital cost
higher magnetic fields economically feasible new research possibilities
Graphics by courtesy of M.N. Wilson
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JE = 375 Amm-2
120mm
≈ 1 MA-turn
≈ 2.5 kW/m
LHC dipole
High current density - dipoles
The field produced by an ideal dipole (see later) is:
JE -JE
Graphics by courtesy of M.N. Wilson
660mm
JE = 37.5 Amm-2
≈ 5x10 MA-turn
≈ 6 MW/m all-SC dipole record field: 16 T (LBNL, 2003)
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Overview
Why superconductors ? A motivation
A superconductor physics primer
Superconducting magnet design Superconducting cables
Superconducting magnets
The making of a superconducting magnet
Uses of superconductivity
A closing word
![Page 7: Introduction to Accelerator Physics Superconducting Magnets · Introduction to Accelerator Physics Superconducting Magnets Luca.Bottura@cern.ch Prague, Czech Republic 31 August -](https://reader031.vdocuments.mx/reader031/viewer/2022040408/5eb93ddd29730e429c60ed22/html5/thumbnails/7.jpg)
A great physics problem in 1900
What is the limit of electrical resistivity at the absolute zero ?
… electrons flowing through a conductor would
come to a complete halt or, in other words, metal
resistivity will become infinity at absolute zero.
“X-rays are an hoax”
“I have not the smallest molecule of faith in aerial navigation other than
ballooning or of expectation of good results from any of the trials we hear of”
"There is nothing new to be discovered in physics now. All that remains is
more and more precise measurement”
W. Thomson (Lord Kelvin)
T
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Superconductors Pre-history
… thus the mercury at 4.2 K has entered a new state, which, owing to its particular electrical properties, can be called the state of superconductivity…
H. Kamerlingh-Onnes (1911)
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Cooper Pairs
Superconductor paired electrons forming
a quasi particle in condensed state
zero resistance because the scattering does not excite the quasi-particle
Normal conductor scattering of e-
finite resistance due to energy dissipation
Bardeen, Cooper and Schrieffer
Proper physics: a gas of Fermions. The conduction electrons at the Fermi surface have large energy (few eV) and interact with lattice defects, displacements or thermal excitations (hence (T))
Proper physics: paired electrons in the vicinity of the Fermi surface, with opposite momentum and spin (bosons with zero spin). The binding energy introduces a small energy gap between paired and unpaired state. An external electric field makes the pair drift.
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Pairing mechanism
Lattice displacement
phonons (sound)
coupling of charge carriers
Only works at low
temperature
Bardeen, Cooper, Schrieffer (BCS) - 1957
t1
t2
100-1000 nm
Proper physics: the binding energy is small, of the order of 10-3 eV. Pairs can be broken easily by thermal energy. The interaction is long range, and Cooper pairs overlap and can exchange electrons
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First (not last) superconducting magnet project cancelled
Solvay conference (1914)
The 10 T magnet project was stopped when it was observed that superconductivity in Hg and Pb was destroyed by the presence of an external magnetic field as small as 500 Gauss (0.05 T)
A 100 kGauss magnet ! (H. K. Onnes)
Third International Congress of Refrigeration, Chicago (1913)
Superconductivity languished for 40 years…
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Flourishing of materials, but depressing Tc…
One Thousand and One Superconductors B. Matthias (1918-1980)
Superconductivity was a physicist playground till the late 1950’s
Theoretical limit around 30 K
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1986 - A Big Surprise
Bednorz and Mueller IBM Zuerich, 1986
1900 1920 1940 1960 1980 2000 0
50
100
150
200
Tem
pera
ture
, T
C (K
)
Year
Low-TC
Hig
h-T
C
164 K
La-214
Hg-1223
Hg V3Si
Graphics by courtesy of P. Grant
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1987 - The prize !
“…for their important break-through in the discovery of superconductivity in ceramic materials”
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High-Tc timeline - impressive !!!
It’s not over yet !
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Hey, what about field ?
Cool down
B
B
Raise field
Meissner & Ochsenfeld, 1933
Type I ( < 1/√2)
Pure metals BC ≈ 10-3…10-2 T
Complete field exclusion
superc
onduct
ing
norm
al-co
nduct
ing
Levitated magnet
Superconducting disk
Example of magnetic levitation
W. Meissner, R. Ochsenfeld
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Free energy and critical field
Let us define the Gibbs free energy of a material in a magnetic field:
A system in equilibrium will tend to a minimum of G
In zero applied field, the SC phase (being in a condensed state) has lower free energy than the normal phase:
The field expulsion (M=-H)
corresponds to a magnetic energy density:
The material prefers to expel the magnetic field (Meissner effect) until the free energy of the SC phase in field equals the free energy of the normal state:
Thermal energy Magnetic energy
G = U - TS - 0 M · H
0/2 Hc2= Gnormal- Gsup(H=0)
Gsup(H=0) < Gnormal(H=0)
-0 M · H = 0/2 H2
Thermodynamic critical field
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Type I – critical field
The difference in free energy DG among the SC
and normal state is small
The corresponding values of the thermodynamic critical field are also small, i.e. in the range of few mT to barely above 100 mT
0/2 Hc2= DG
Not very useful for magnet engineers !
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London penetration length L
Field profile
London penetration length
H. and F. London, 1935
L is of the order of 20 to 100 nm in typical superconducting materials
B
x L
Normal phase
Superconducting phase
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is of the order of 1 to 1000 nm in typical superconducting elements and alloys
nS
x
Normal phase
Superconducting phase
Coherence length
At an interface the density of paired electron nS rises
smoothly from zero (at the surface) to the asymptotic value (in the bulk)
The characteristic length of this transition is the coherence length
Fermi velocity
SC energy gap
Ginzburg–Landau, 1950
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Energy efficient fluxons
Meissner & Ochsenfeld, 1933
Type I ( < 1/√2)
Pure metals BC ≈ 10-3…10-2 T
Complete field exclusion
Type II ( > 1/√2)
Dirty materials: alloys intermetallic, ceramic
BC ≈ 10…102 T
Ginsburg, Landau, Abrikosov, Gor’kov, 1950…1957
Partial field exclusion Lattice of fluxons
Landau, Ginzburg and Abrikosov
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Values of L , and
Material L
(nm)
(B=0)
(nm)
(-)
Al 16 1600 0.01
Pb 32 510 0.06
In 24 360 0.07
Cd 110 760 0.15
Sn 30 170 0.18
Nb 40 39 1
Nb3Sn 200 12 ≈ 20
MgB2 185 5 ≈ 40
YBCO 200 1.5 ≈ 75
Type I
Type II
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Lattice of quantum flux lines
Observation on Pb-4at% In magnetised by a field of 3000 Oe and decorated by Co particles
Essmann & Träuble, 1967
0 = h/2e = 2.07 x 10-15 Wb
Flux quantum
Supercurrent
Graphics by courtesy of Superconductor Lab, Oslo
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Tc(K)
Type II – critical field
NOTE: of all the metallic
superconductors, only
NbTi is ductile.
All other are brittle inter-
metallic compounds
The upper critical field BC2 and temperature TC of metallic superconductors are mutually related
Both BC2 and TC are determined by the chemistry of the material
HTS
Graphics by courtesy of M.N. Wilson
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Hey, what about current ?
A current flowing in a magnetic field is subject to the Lorentz force that deviates the charge carriers:
F = J x B
This translates into a motion of the fluxoids across the superconductor energy dissipation loss of superconductivity
To carry a significant current we need to lock the fluxoids so to resist the Lorentz force. For this we mess-up the material and create pinning centers that exert a pinning force FP
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Pinning centers
Microstructure of Nb-Ti
Graphics by courtesy of Applied Superconductivity Center at NHMFL
Precipitates in alloys
Grain boundaries in inter-metallic compounds
Microstructure of Nb3Sn
grain
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Jc(B,T,…)
B [T]
T [K]
Jc [A/mm2]
5
5
100
1,000
10,000
100,000
10 10
15
T=1.9 K
T=4.2 K
The maximum current that can be carried by the superconductor is the current at which:
|J x B| = FP
The above expression defines a critical surface:
JC(B,T,…) = FP / B
Critical surface of a LHC NbTi wire
Jc (5 T, 4.2 K) ≈ 3000 A/mm2
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Superconductors – the bottom line
Superconducting materials are only useful if they are dirty (type II - high critical field) and messy (strong pinning centers)
A superconductor is such only in conditions of temperature, field and current density within the critical surface, and it is a normal-conductor above these conditions. The transition is defined by a critical current density JC(B,T,…)
The maximum current that can be carried is the IC = ASC x JC
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Overview
Why superconductors ? A motivation
A superconductor physics primer
Superconducting magnet design Superconducting cables
Superconducting magnets
The making of a superconducting magnet
Uses of superconductivity
A closing word
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From materials to magnets
Materials must be made in high-current wires, tapes and cables for use in magnets
The manufacturing route depends, among others on: The material (e.g. alloy or chemical compound),
The material synthesis (e.g. reaction conditions or a crystal growth method)
The material mechanical properties (e.g. ductile or fragile)
The compatibility with other materials involved (e.g. precursors or mechanical supports)
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A summary of technical materials
Tevatron HERA RHIC LHC
HL-LHC Power transmission cables and SC links
20 T and beyond !
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Nb-Ti manufacturing route
extrusion cold drawing
heat treatments
NbTi is a ductile alloy that can sustain large deformations
IC(5 T, 4.2 K) ≈ 1 kA NbTi billet
Graphics by courtesy of Applied Superconductivity Center at NHMFL
1 m
m
LHC wire
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Nb3Sn manufacturing routes
Nb3Sn is brittle and cannot be drawn in final form. The precursors are drawn and only later the wire is heat-treated to ≈650 C for several hrs, to form the Nb3Sn phase
Graphics by courtesy of Applied Superconductivity Center at NHMFL
IC(12 T, 4.2 K) ≈ 1.5 kA
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Oxide powder in tube OPIT
1) draw down BSCCO
powder in a silver
tube
2) stack many drawn
wires in another silver
tube and draw down
again
3) roll the final wire to tape and heat treat at
800 - 900C in oxygen to melt the B2212
BSCCO manufacturing routes
BSCCO is also brittle: a special sequence of rolling and sintering heat treatments must used. Silver has the important feature that it is transparent to Oxygen at high temperature, but does not react with it
BSCCO wire and tape
Graphics by courtesy of M.N. Wilson and Applied Superconductivity Center at NHMFL
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• produce a tape with an aligned texture
• coat the tape with a buffer layer
• coat the buffer with a layer YBa2Cu3O7
such that the texture of the YBCO
follows that of the buffer and substrate
All routes use a ion
deposition techniques (laser,
plasma, evaporation) in
vacuum (cost & length !)
YBa2Cu3O7
YBCO tape (developmental)
YBCO has excellent critical properties, but grains do not
align during processing. If grains are not aligned the supercurrent
cannot jump between the grains. All manufacturing processes
force a certain degree of alignment in the microstructure
Buffer
layer Textured
tape
1
m
≈0.1
mm
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Practical conductors: high JE
Multifilamentary wires have current carrying capability of 100… 1000 A
Insulated with varnish or glass-braids they can be used to make all kind of small size magnets
Large size magnets (e.g. LHC dipoles) require invariably large operating currents (10 to 100 kA) to:
Decrease inductance,
Lower the operating voltage,
Ease magnet protection
Rutherford cables are ideally suited for this task
JE ≈ 500 A/mm2
LHC cable prototype
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Rutherford cable machine @ CERN
Strand spools on rotating tables
Strands fed through a cabling tongue to shaping
rollers
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we expect the magnet to go resistive i.e. to 'quench', where the peak field load line crosses the critical current line
8
6
4 2 2
4
6
8 10
12 14
1
2
3
4
5
6
7
Curr
ent
den
sity
kA
/mm
2
10
Peak field
5 T Bore field
Critical line and magnet load lines
NbTi critical current
IC(B)
quench !
NbTi critical surface e.g. a 5 T magnet design
IC = JC x ASC
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Current quench IQ
Field quench BQ
Loadline quench Imax
Temperature quench TCS
Operating margins
Practical operation always requires margins: Critical current margin:
Iop/IQ ≈ 50 %
Critical field margin: Bop/BQ ≈ 75 %
Margin along the loadline: Iop/Imax ≈ 85 %
Temperature margin: TCS - Top ≈ 1…2 K
The margin needed depends on the design and operating conditions
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Engineering current density
All wires, tapes and cables contain additional components: Left-overs from the precursors of the SC formation
Barriers, texturing and buffering layers
Low resistance matrices
The SC material fraction is hence always < 1:
= ASC / Atotal
To compare materials on the same basis, we use an engineering current density:
JE = JC x
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Best of Superconductors JE
Graphics by courtesy of Applied Superconductivity Center at NHMFL
useful JE
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Perturbation spectrum
mechanical events wire motion under Lorentz force, micro-slips
winding deformations
failures (at insulation bonding, material yeld)
electromagnetic events flux-jumps (important for large filaments, old story !)
AC loss (most magnet types)
current sharing in cables through distribution/redistribution
thermal events current leads, instrumentation wires
heat leaks through thermal insulation, degraded cooling
nuclear events particle showers in particle accelerator magnets
neutron flux in fusion experiments
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Perturbation overview
Typical range is from a few to a few tens of mJ/cm3
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Stability as a heat balance
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A prototype temperature transient
heat pulse…
…effect of heat conduction and cooling…
generation>cooling unstable
generation<cooling stable
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Stability - Re-cap
A sound design is such that the expected energy spectrum is smaller than the expected stability margin
To increase stability: Increase temperature margin
Increase heat removal (e.g. conduction or heat transfer)
Decrease Joule heating by using a stabilizer with low electrical conductance
Make best use of heat capacity Avoid sub-cooling (heat capacity increases with T, this is
why stability is not an issue for HTS materials)
Access to helium for low operating temperatures
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What if we exceed the limits ? Quench !
A resistive transition in a superconducting magnet, leading to appearance of voltage, Joule heating, temperature increase, thermal and electro-magnetic forces, and cryogen expulsion.
This is a quench of a GE MRI magnet during tests at the plant
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Stored energy
The energy stored in the magnetic field of accelerator dipoles scales with the square of the bore field
A large stored magnetic energy makes the magnet difficult to protect, and requires:
Fast detection and dump
High terminal voltage and operating current
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Energy dissipation
the magnetic energy stored in the field:
is converted to heat through Joule heating RI2. If this process happened uniformly in the winding pack:
Cu melting temperature 1356 K
corresponding Em=5.2 109 J/m3
limit would be Bmax 115 T: NO PROBLEM !
BUT
the process does not happen uniformly (as little as 1 % of mass can absorb total energy)
L
R
2
0
2
2
1
2LIdv
BE
V
m == ò m
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Issues to be considered
Temperature increase and temperature gradients (thermal stresses)
Voltages within the magnet, and from the magnet to ground (whole circuit)
Forces caused by thermal and electromagnetic loads during the magnet discharge transient
Cryogen pressure increase and expulsion
A quench invariably requires detection and may need actions to safely turn-off the power supply (possibly
more)
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Hot-spot limits
the quench starts in a point and propagates with a quench propagation velocity
the initial point will be the hot spot at temperature Tmax
Tmax must be limited to: limit thermal stresses (see
graph)
avoid material damage (e.g. resins have typical Tcure 100…200 °C)
Tmax < 100 K for negligible effect
Tmax < 300 K for highly supported coils
(e.g. accelerator magnets)
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Detection, switch and dump
precursor
propagation
detection
detection threshold
trigger (t=0)
fire heaters
switch dump
dump
discharge ≈ detection + delay + switch + dump
By courtesy of M. Di Castro, CERN AT-MTM, 2007.
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Quench resistance
the quench propagates in the coil at speed vquench longitudinally (vlongitudinal) and transversely (vtransverse)…
…the total resistance of the normal zone Rquench(t) grows in time following
the temperature increase, and
the normal zone evolution…
…a resistive voltage Vquench(t) appears along the normal zone…
…that dissipates the magnetic energy stored in the field, thus leading to a discharge of the system in a time discharge.
the knowledge of Rquench(t) is mandatory to verify the protection of the magnetic system !
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( ) 2
0
2
2
1opop LIdtItR
decay
³òt
Quench protection
The magnet stores a magnetic energy 1/2 L I2
During a quench it dissipates a power R I2 for a duration decay characteristic of the powering circuit
initial magnetic energy
total dissipated resistive power during decay
yes no
self-protected: detect, switch-off power and
let it go… most likely OK
WARNING: the reasoning here is qualitative, conclusions require in any case detailed checking
requires protection: detect, switch-off power and
do something !
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Energy dump
the magnetic energy is extracted from the magnet and dissipated in an external resistor:
the integral of the current:
can be made small by: fast detection
fast dump (large Rdump)
B.J. Maddock, G.B. James, Proc. Inst. Electr. Eng., 115, 543, 1968
L
Rquench
Rdump
S
normal operation
quench
quenchdump RR >>
( )
dump
detectiont
opeIIt
t--
=dump
dumpR
L=t
÷÷ø
öççè
æ+»ò
¥
2
2
0
2 dump
detectionopJdtJt
t
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Dump time constant
magnetic energy:
maximum terminal voltage:
dump time constant:
opdump IRV =max
2
2
1opm LIE =
op
m
dump
dumpIV
E
R
L
max
2==t
operating current maximum terminal
voltage
interesting alternative: non-linear Rdump or voltage source
increase Vmax and Iop to achieve fast dump time
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Quench heaters
the quench is spread actively by firing heaters embedded in the winding pack, in close vicinity to the conductor
winding
heater
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Magnet strings
magnet strings (e.g. accelerator magnets, fusion magnetic systems) have exceedingly large stored energy (10’s of GJ):
energy dump takes very long time (10…100 s)
the magnet string is subdivided and each magnet is by-passed by a diode (or thyristor)
the diode acts as a shunt during the discharge
M3 M3 M1 M2 MN
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Quench - Re-cap
A good conducting material (Ag, Al, Cu: large Z(Tmax)) must be added in parallel to the superconductor to limit the maximum temperature during a quench
The effect of a quench can be mitigated by Adding stabilizer ( operating margin, stability)
Reducing operating current density ( economics of the system)
Reducing the magnet inductance (large cable current), increasing the discharge voltage and subdividing (strings) to discharge the magnet as quickly as practical
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Overview
Why superconductors ? A motivation
A superconductor physics primer
Superconducting magnet design Superconducting cables
Superconducting magnets
The making of a superconducting magnet
Uses of superconductivity
A closing word
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Magnetic design - basics
NC: magneto motive force, reluctance and pole shapes
SC: Biot-Savart law and coil shapes
B ≈ 0 NI / g
B g
g =100 mm NI =100 kAturn B =1.25 T
Hopkinson's law
+I -I
+I -I +I -I
B
Biot-Savart law
B ≈ 0 NI / r
r
r =45 mm NI =1 MAturn B =8.84 T
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Design of an ideal dipole magnet
I=I0 cos() Intersecting circles
Intersecting ellipses
B1=-0 I0/2 r B1=-0 J d/2
+J -J
d
B1=-0 J d b/(a+b)
r
+J -J
d a
b Several solutions are possible and can be extended to higher order multi-pole magnets None of them is practical !
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Magnetic design - sector coils
Dipole coil Quadrupole coil
Rin Rout
+J -J
Rin Rout
+J
-J
+J
-J B=-20/ J (Rout - Rin) sin()
This is getting much more practical !
G=-20/ J ln(Rout/Rin) sin(2)
The field is proportional to the current density J and the coil width (Rout-Rin)
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Evolution of coil cross sections
Coil cross sections (to scale) of the four superconducting colliders
Increased coil complexity (nested layers, wedges and coil blocks) to achieve higher efficiency and improved field homogeneity
Tevatron HERA RHIC LHC
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Technical coil windings
Magnet bore
Superconducting cable
Coil blocks
Spacers
LHC arc dipole LHC arc quadrupole
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Iron to close the magnetic circuit
flux lines
gap between coil and yoke
coil
CERN 87-05, G. Brianti and K. Hubner Ed. G. Brianti
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Persistent currents - basics
H. Brück, et al., Z. Phys. C, Particles and Fields, 44, pp. 385-392, 1989
Eddy currents that flow in the superconducting filaments to shield the interior from outer field variations
For accelerator magnets: Neglect flux-creep and flow
Neglect outer field changes (decay at I=const)
Infinite time constant,
the eddy currents last forever
Persistent currents
B
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B
Persistent currents - basics
The current doublet in the filament corresponds to a magnetization:
A strand, with round filaments in a resistive matrix ( = ASC/Atot), fully penetrated:
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Persistent current multipoles
Magnetization of a typical LHC strand
Sextupole in a typical LHC dipole
Effects are relatively large, cycle and history dependent and require careful design, measurement and control !
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A matter of (field) quality The field homogeneity for an accelerator magnet needs to
be in the 100 ppm range (at 1 cm from the coil)
Type of error Origin Effect on main field
Effect on harmonics
Means to control
geometric Deviation of conductor from ideal position
10-4 10-4 Respect coil tolerances at 10 m level
saturation Iron saturation in vicinity of the coil
10-2 to 10-3
10-4 Optimize iron geometry,
control permeability to % level
DC magnetization
Diamagnetism of SC filaments and hysteresis
10-3 to 10-4
10-3 to 10-
4
Use small filaments (10…20 m) and control wire magnetization homogeneity
AC magnetization
Coupling currents in strands and cables
10-3 to 10-4 10-4 Use resistive matrix in strands (ramped magnets), control strands coupling in cable (Rc ≥ 10 W)
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Electromagnetic force
An electric charged particle q moving with a velocity v in a field B experiences a force FL called electromagnetic (Lorentz) force (N):
A conductor carrying current density J (A/mm2) experiences a (Laplace) force density fL (N/m3):
BvqFL
BJf L
(O. Heaviside) E.A. Lorentz, P.S. Laplace
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Electromagnetic forces - dipole
The electromagnetic forces in a dipole magnet tend to push the coil:
Vertically, towards the mid plane (Fy < 0)
Horizontally, outwards (Fx > 0)
Tevatron dipole
Fy
Fx
Field Force
Graphics by courtesy of P. Ferracin, S. Prestemon, E. Todesco
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Electromagnetic forces - ends
In the coil ends the Lorentz forces tend to push the coil:
Outwards in the longitudinal direction (Fz > 0), and, similar to solenoids, the coil straight section is in tension
Fz
Graphics by courtesy of P. Ferracin, S. Prestemon, E. Todesco
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The real challenge of very high fields
Force increases with the square of the bore field Requires massive
structures (high-strength materials, volume, weight)
The stress limit is usually in the superconducting coil (superconductor and insulation, mitigated by Je≈1/B)
In practice the design of high field magnets is limited by mechanics
Force per coil quadrant in high-field dipoles built or designed for
accelerators applications and R&D
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Overview
Why superconductors ? A motivation
A superconductor physics primer
Superconducting magnet design Superconducting cables
Superconducting magnets
The making of a superconducting magnet
Uses of superconductivity
A closing word
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LHC dipole
Bnominal 8.3 (T) current 11850 (A) stored energy 10 (MJ) cold mass 35 (tonnes)
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Rutherford cables
LHC Nb-Ti strand LHC inner cable
LHC outer cable cross section
7500 km of superconducting cables with tightly controlled properties (state-of-the-art production)
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Coil winding
B B
Cable insulation wraps
Coil winding machine
Stored coils
Insulated cable
Bare cable
10 m precision !
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Ends
Inner layer
Layer jump
Ends, transitions, and any deviation from the regular structure are the most delicate part of the magnet
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Collaring operation
Pre-collared coil assembly under a press, load the coil to the desired pre-stress (in the range of 50…100 MPa)
Insert keys to “lock” the collars, unload the assembly
that is now self-supporting and provides the desired
pre-load to the coil
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Collaring of an LHC dipole
Collaring force: 1400 tons/m Maximum press force: 37500 tons
76 hydraulic cylinders (600 bar) Planarity ±0.3 mm/m
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LHC dipole coils
B B
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LHC Iron yoke
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“Yoking” of a dipole magnet
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Yoke welding press
yoking
Yoking force: 400 tons/m Maximum press force: 19000 tons 48 hydraulic cylinders (600 bar)
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Cold mass
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Cryostat
Vacuum enclosure
Low conduction foot
Thermal screens
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Finally, in the tunnel !
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Overview
Why superconductors ? A motivation
A superconductor physics primer
Superconducting magnet design Superconducting cables
Superconducting magnets
The making of a superconducting magnet
Uses of superconductivity
A closing word
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The Hall of Fame of SC colliders
Tevatron HERA RHIC LHC
Maximum energy (GeV) 980 920(1) 250(2) 100/n(3)
7000
Injection energy (GeV) 151 45 12 450
Ring length (km) 6.3 6.3 3.8 26.7
Dipole field (T) 4.3 5.0 3.5 8.3
Aperture (mm) 76 75 80 56
Configuration Single bore Single bore Single bore Twin bore
Operating temperature
(K) 4.2 4.5 4.3-4.6 1.9
First beam 7-1983 4-1991 6-2000 9-2008
(1) energy of the proton beam, colliding with the 27.5 GeV electron beam (2) energy for proton beams (3) energy per nucleon, for ion beams (Au)
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Champion dipoles cross sections
HERA Bore: 75 mm Field: 5.0 T
Tevatron Bore: 76 mm Field: 4.3 T
RHIC Bore: 80 mm Field: 3.5 T
LHC Bore: 56 mm Field: 8.3 T
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Tevatron at FNAL (Chicago, IL, USA)
Injection (GeV) 151
Flat-top (GeV) 980
Length (km) 6.3
Dipole field (T) 4.3
Aperture (mm) 76
Temperature (K) 4.2
Commisioned 1983
Image by courtesy of Fermi National Accelerator Laboratory
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HERA at DESY (Hamburg, D)
Injection (GeV) 45
Flat-top (GeV) 920
Length (km) 6.3
Dipole field (T) 4.7
Aperture (mm) 75
Temperature (K) 4.5
Commisioned 1991
Closed 2007
Image by courtesy of Deutsches Elektronen Synchrotron
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RHIC at BNL (Upton, NY, USA)
Injection (GeV) 12/n
Flat-top (GeV) 100/n
Length (km) 3.8
Dipole field (T) 3.5
Aperture (mm) 80
Temperature (K) 4.3-4.6
Commisioned 2000
Image by courtesy of BrookhavenAccelerator Laboratory
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LHC at CERN (Geneva, CH)
Injection (GeV) 450
Flat-top (TeV) 7
Length (km) 26.7
Dipole field (T) 8.3
Aperture (mm) 56
Temperature (K) 1.9
Commisioned 2008
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Magnetic Resonance Imaging (MRI)
patient's view
engineer's view
surgeon's
view
photos courtesy of
SIEMENS
Magnet Technology
photo courtesy of
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NMR spectroscopy
Magnet Technology
photo courtesy of
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Motors & generators
700 MW generator
NbTi rotor
Hitachi, Toshiba, Mitsubishi
Motor with HTS rotor
American Superconductor and
Reliance
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Transformers & energy storage
Toroidal magnet of 200 kJ / 160 kW
energy store
(B = 4 T, dia. = 1.1 m)
KfZ Karlsruhe
HTS Transformer
630 kVA, 18.7kV to 0.42 kV
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Magnetic separation
superconducting
solenoid,
enclosed within
iron shield
stainless steel
canister
containing
ferromagnetic
mesh
pipes feeding
the kaolin slurry
for separation
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PF1
PF2
PF3
PF4
PF5
PF6
ITER
International Thermonuclear Experimental Reactor
CS
TF
Thermonuclear fusion
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Omega BEBC
HEP detectors of the past...
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… and HEP of the present (CMS and ATLAS)
CMS ATLAS
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Levitation…
JR-Maglev MLX01 581 km/h (Dec. 2003)
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… more levitation
Water A frog
Diamagnetic levitation in strong magnetic fields (16 T) as can
be produced by superconductin and hybrid magnets
Nuts
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Other uses of superconductivity
Letter to Prof. Main, University of Nottingham, 14 April 1997
The Church of the Latter Day Snakes founded 1905, revived 1950
We have a big interest
in this machine…
How big is this magnet, and can it be
concealed beneath a floor…
Does it make much noise…
Does it hurt… because it will
be me doing the levitating.
…we pull back the curtain in the
Snake Chamber and I start to rise up
from the ground…
Tsonaoumi, 202 Kg
I put in five pounds for you…
This is only the start.
…the Natural Law Party… please do
not sell them a machine… they are
very bonkers…
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Overview
Why superconductors ? A motivation
A superconductor physics primer
Superconducting magnet design Superconducting cables
Superconducting magnets
The making of a superconducting magnet
Uses of superconductivity
A closing word
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A word of closing
Superconducting magnet design is a lot about superconductors (materials, wires, cables, and their electric and thermal properties)…
… but not only !
High field & forces bear mechanical problems that are tough to solve (B=10 T pmag=400 bar !)
Materials at low temperature are not what we are used to (mechanical and magnetic properties, thermal expansion, electrical insulation)
Cooling is an applied science by itself
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Where to find out more - 1/3
Superconducting magnets: Case Studies in Superconducting Magnets: Y. Iwasa, Plenum Press, New York
(1994), ISBN 0-306-44881-5.
Superconducting Magnets: M.N. Wilson, Oxford University Press (1983) ISBN 0-019-854805-2
High Field Superconducting Magnets: F.M. Asner, Oxford University Press (1999) ISBN 0 19 851764 5
Superconducting Accelerator Magnets: K.H. Mess, P. Schmuser, S. Wolf, World Scientific, (1996) ISBN 981-02-2790-6
Stability of Superconductors: L. Dresner, Plenum Press, New York (1994), ISBN 0-306-45030-5
Handbook of Applied Superconductivity ed. B. Seeber, UK Institute Physics 1998
Proc Applied Superconductivity Conference: IEEE Trans Magnetics, 1975 to 1991, and IEEE Trans Applied Superconductivity, 1993 to 2012,
Proc European Conference on Applied Superconductivity EUCAS, UK Institute Physics
Proc International Conference on Magnet Technology; MT-1 to MT-20 (2007) mainly as IEEE Trans Applied Superconductivity and IEEE Trans Magnetics
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Where to find out more - 2/3
Cryogenics Helium Cryogenics S.W. Van Sciver, Plenum Press, 86 ISBN 0-
0306-42335-9
Cryogenic Engineering, B.A. Hands, Academic Press 86 ISBN 0-012-322991-X
Cryogenics: published monthly by Elsevier
Materials - Superconducting properties Superconductor Science and Technology, published monthly
by Institute of Physics (UK).
IEEE Trans Applied Superconductivity, published quarterly
Superconductivity of metals and Cuprates, J.R. Waldram, Institute of Physics Publishing (1996) ISBN 0 85274 337 8
High Temperature Superconductors: Processing and Science, A. Bourdillon and N.X. Tan Bourdillon, Academic Press, ISBN 0 12 117680 0
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Where to find out more - 3/3
Materials - Mechanical properties
Materials at Low Temperature, Ed. R.P. Reed and A.F. Clark, Am. Soc. Metals 1983. ISBN 0-87170-146-4
Handbook on Materials for Superconducting Machinery, Batelle Columbus Laboratories, 1977.
Nonmetallic materials and composites at low temperatures, Ed. A.F. Clark, R.P. Reed, G. Hartwig, Plenum Press
Nonmetallic materials and composites at low temperatures 2, Ed. G. Hartwig, D. Evans, Plenum Press, 1982